Growing crystals is never quick. The slower you increase supersaturation, the better the crystals. Ideally, choose a solvent where you can fully dissolve the material at elevated temp. Then let it cool as slowly as you can. If leaving it on the bench is too fast you'll have many nucleation sites and hence more likely to make a powder, then cool more gently on a hotplate. Try to minimise evaporation while you do this to prevent even more rapid supersaturation. May take a while but will be worth it.